Enhanced Brightness and Efficiency in Next-Generation LEDs: A Stanford Discovery, But With a Price

Stanford University researchers have been working on eight green perovskite LED materials, shining ultraviolet light on them to generate a glow. Image Credit: Sebastian Fernández / Stanford University

A Molecular Addition Improves Next-Generation LEDs, Despite Reducing Their Durability

By modifying the composition of perovskite LEDs, a more affordable and simpler LED variant, the researchers at Stanford managed to make significant advances in brightness and efficiency. Unfortunately, these lights would fail after only a brief period of use.

Light-emitting diodes, or LEDs, are the primary source of illumination in screens that you likely use daily. These offer energy-saving indoor lighting and are increasingly found in computer monitors, TVs, and mobile devices. However, their manufacture is somewhat complex and costly.

Stanford’s Exploration for Accessible and Efficient Illumination

To mitigate this issue, Stanford’s research team experimented with enhancing the brightness and efficiency of perovskite LEDs (PeLEDs), an economical and simpler-to-manufacture alternative. While these improvements led to a temporary increase in performance, the lights would quickly deteriorate, indicating the delicate balance required to progress this material category.

“We made significant strides in comprehending the degradation. The challenge is how to curb that while maintaining efficiency,” states Dan Congreve, assistant professor of electrical engineering and senior author of the paper published recently in the journal Device. “If we can achieve that, we may indeed be on the path to a feasible commercial application.”

Eight green manganese-infused perovskite LEDs glowed in Congreve’s laboratory as an electric current was applied. Image Credit: Sebastian Fernández / Stanford University

Understanding What Sets Perovskite LEDs Apart

LEDs convert electrical power into light through an electric current passing through a semiconductor—layers of crystalline substance that emit light under an electrical field. However, constructing these semiconductors can become intricate and expensive compared to less efficient lighting technologies like incandescents and fluorescents.

“Many of these materials are cultivated on high-cost surfaces like a four-inch sapphire substrate,” explains Sebastian Fernández, a PhD student in Congreve’s lab and the paper’s lead author. “The substrate alone can cost several hundred dollars.”

PeLEDs are made of a semiconductor known as metal halide perovskites, comprised of different elements. This enables engineers to grow perovskite crystals on glass, leading to considerable savings. Additionally, the perovskites can be dissolved and “painted” onto glass to form a luminescent layer, further simplifying the process compared to conventional LEDs.

The Potential and Restrictions of Perovskite LEDs

These benefits might make energy-conserving indoor lighting more attainable, cutting down energy requirements. PeLEDs might also improve the color clarity of mobile and television screens. “The greens are greener, the blues are bluer,” remarks Congreve. “The device literally displays a broader color spectrum.”

However, most PeLEDs currently falter after just a few hours and usually don’t match the energy efficacy of regular LEDs, mainly due to inconsistencies or ‘defects’ within the perovskite’s atomic arrangement. “An atom should be here, but it isn’t,” explains Congreve. “Energy enters there, but light doesn’t emerge, reducing the device’s overall effectiveness.”

Balancing Brightness with Durability

To alleviate these problems, Fernández expanded on a method pioneered by Congreve and Mahesh Gangishetty, assistant professor of chemistry at Mississippi State University and paper co-author. By substituting 30% of the perovskite’s lead with manganese, filling those gaps, they more than doubled the PeLEDs’ brightness, nearly tripled efficiency, and extended the life from less than a minute to 37 minutes.

This method also may reduce health hazards. “Lead is vital for this material’s light emission, but is also known to be toxic,” Fernández says. Its water-solubility could also lead to leakage through a cracked screen. “This pushes me to think about alternative materials.”

Ongoing Developments and Challenges

Fernández also incorporated a phosphine oxide called TFPPO into the perovskite. “I added it and saw the efficiencies skyrocket,” he claims. The additive increased energy efficiency by up to five times compared to only manganese enhancement and produced some of the brightest PeLEDs ever seen.

But this came with a drawback: the brightness halved within two and a half minutes (while the perovskites without TFPPO lasted for 37 minutes).

Assessing the Compromise

Fernández believes that in PeLEDs with TFPPO, the transformation of electrical energy to light over time becomes less effective, primarily due to challenges tied to charge transport within the PeLED. The team also theorizes that while TFPPO initially fills gaps in the atomic structure, they quickly reopen, resulting in a decline in both energy efficiency and longevity.

In the future, Fernández plans to test other phosphine oxide additives to investigate their different impacts and reasons.

“This additive is extraordinary in terms of efficiency,” states Fernández. “However, we must overcome its effects on stability if we are to consider commercializing this material.”

Congreve’s lab is also addressing other PeLED limitations, such as the difficulty in producing violet and ultraviolet light. In another recent publication in the journal Matter, the team discovered that by adding water to the perovskite crystal solution, they could create PeLEDs emitting bright violet light five times more efficiently. With further enhancements, ultraviolet PeLEDs could sterilize medical instruments, cleanse water, and assist in indoor agriculture, all at a more affordable rate than current LEDs.

Reference: “Trade-off between efficiency and stability in Mn2+-doped perovskite light-emitting diodes” by Sebastian Fernández, William Michaels, Manchen Hu, Pournima Narayanan, Natalia Murrietta, Arynn O. Gallegos, Ghada H. Ahmed, Junrui Lyu, Mahesh K. Gangishetty, and Daniel N. Congreve, 1 August 2023, Device.
DOI: 10.1016/j.device.2023.100017

Additional collaborators on this research at Stanford include undergraduate student William Michaels, graduate students Pournima Narayanan, Natalia Murrietta, Arynn Gallegos, postdoctoral researcher Ghada Ahmed, and graduate student Junrui Lyu.

This study was supported by the Diversifying Academia, Recruiting Excellence (DARE) Fellowship, the U.S. Department of Energy, Stanford Graduate Fellowships in Science & Engineering (P. Michael Farmwald Fellow, Gabilan Fellow, and Scott A. and Geraldine D. Macomber Fellow), the National GEM Consortium, the Department of Electrical Engineering at Stanford University, and the National Science Foundation. Parts of this project were carried out at the Stanford Nano Shared Facilities, backed by the National Science Foundation.

Frequently Asked Questions (FAQs) about perovskite LEDs

More about perovskite LEDs

• Stanford University
• Journal of Device
• U.S. Department of Energy
• National Science Foundation
• Stanford Graduate Fellowships in Science & Engineering
• Stanford Nano Shared Facilities